energy

1) Explain Energy
  • Amount of work done = energy transferred.
  • SI unit for energy is Joules (J).
  • The sun is the source of energy for all our energy resources except geothermal, nuclear and tidal.
  • In the sun, energy is created through a process called nuclear fusion: hydrogen nuclei are pushed together to form helium.
  • ​The moon is the main source of tidal energy. 
  • Energy can be transferred between different forms including kinetic, gravitational potential, chemical, elastic potential, nuclear and internal energy as a result of an event or process.
  • An object may have energy due to its motion (KE) or its position (PE), and that energy may be transferred and stored.
Kinetic energy:
\[K.E.=\frac{1}{2}mv^{2}\]
Gravitational potential energy: G.P.E = m g h
  • Work is done when a force moves something through a distance. The work done is equal to the energy transferred.
​work done = energy transferred
Energy type
What it is
Example
Kinetic
Due to motion
Moving objects
Gravitational
Due to position (height)
Objects lifted to a certain height
Chemical
In chemicals
Batteries
Elastic
Due to stretch
Elastic band
Nuclear
Due to atoms rearranged/split
Nuclear plant
Electrical
Carried by electrons
Electricity
Light
Carried in light waves
From sun
Sound
Carried in sound waves
From speaker
2) Conservation of Energy
  • ​Energy cannot be created or destroyed, when work is done, energy is changed from one form to another.
  • Example of conversion of energy: A book on a shelf has g.p.e , if it falls of the shelf it will have k.e.
  • Due to the processes through which energy transfers take place not being 100% efficient, energy is lost to the surrounding and therefore energy gets more spread out (dissipated).
3) Efficiency:
How much useful work is done with energy supplied
4) Energy Resources
Non-renewable sources of energy: are exhaustible
Type
Advantages
Disadvantages
​Fuel: burnt to make thermal energy, makes steam, turns turbine
Cheap. Plentiful. Low-tech
Harmful wastes:
Greenhouse/pollutant gas
Renewable sources: are not exhaustible
Type
Advantages
Disadvantages
Wave energy: generators driven by up and down motion of waves at sea.
No greenhouse gases produced
Difficult to build
Tidal energy: dam built where river meets sea, lake fills when tides comes in & empties when tide goes out; water flow runs generator
No greenhouse gases produced
Expensive. Can’t be built everywhere
Hydroelectric: river & rain fill up lake behind dam, water released, turns turbine ​generator
Low impact on environment. Energy produced at constant rate
Few areas in the world suitable
Nuclear fission: uranium atoms split by shooting neutrons at them
Produces a lot of energy with very little resources
Produces radioactive waste
Wind: windmills are moved by the breeze. They generate electricity from kinetic energy
No CO2/Greenhouse gases produced
Few areas in the world suitable
​ Solar cells/photovoltaic cells: made of materials that deliver electrical current when it absorbs light  
Solar Panels: absorbs energy and use it to heat water
No CO2 produced
Variable amount of sunshine in some countries
​

work and power

  • Work done is the same as energy transferred.
  • Conservation of energy links GPE, KE and work done.
  • Power is the rate of transfer of energy or the rate of doing work.
work done = Force x distance moved in the direction of the force
W = F d =  E
5) Work
  • Work is done whenever a force makes something move.
  • The unit for work is the Joule (J).
Work Done = Force x Distance moved in the direction of the Force
W = F x D
6) Power
Power is a measure of how quickly work is being done and so how quickly energy is being transferred.
The unit for power is Watts (W)
​1 W = 1 J/s
\[P=\frac{E}{t}\]
​in simple systems, including electrical circuits